Shear Wave UT – Calibration

Shear wave UT is calibrated using a test block manufactured from a material similar to the workpiece (i.e., with the same velocity of sound), that has side-drilled holes and a notch on the back surface as shown in Figure 700-18. The test block should have a thickness within 1 inch of the thickness of the workpiece. The side-drilled holes should be 3/16-inch diameter for test blocks up to 4 inches thick, and increase 1/16-inch in diameter for each 2-inch increase in thickness of the test block greater than 4 inches.

The transducer is first moved along the surface until the reflection from the ¼-thickness drill hole attains maximum peak amplitude at the position of Transducer A in Figure 700-18, and the delay control on the ultrasonic instrument is adjusted to shift the peak to a distance on the oscilloscope display equal to the depth of the hole from the surface.

Calibration of Shear Wave UT

Next, the transducer is moved along the surface until the reflection from the ¾-thickness drill hole attains maximum peak amplitude at the position of Transducer C, and the material velocity control on the ultrasonic instrument is adjusted until the peak coincides with the distance on the oscilloscope display corresponding to the depth of this hole from the surface. Moving the transducer along the surface until a reflection of maximum peak amplitude is obtained from the ½-thickness hole at the position of Transducer B should produce this peak at a distance in the oscilloscope display corresponding to the depth of this hole below the surface.

Then, the transducer is moved until a reflection of maximum peak amplitude is obtained from the ¾-thickness hole when the ultrasonic shear wave is reflected by the back surface of the test block at the position of Transducer E. This peak should appear in the oscilloscope display at a distance corresponding to 5/4 the thickness of the test block. The maximum peak amplitudes determined in this manner will establish a distance amplitude curve (DAC) for shear wave UT. The sensitivity control on the ultrasonic instrument should be adjusted until the amplitude of the highest peak is at least 80% of the oscilloscope screen height.

A very strong reflection is normally obtained from the notch on the back surface with an ultrasonic shear wave at 45 degrees, which can exceed the DAC. However, ultrasonic shear waves at 60 degrees and 70 degrees will usually produce reflections from the notch that are below the DAC.


Categories: In-Service Inspection | Tags: , | Leave a comment